Thin film coating of pharmaceutical tablets allows efficient, controlled, uniform and reproducible coats. Use of multiple layers of coating, such as the polymeric undercoat, polymeric pigmented second coat and polymeric finish coat allows the preparation of very smooth glossy tablets (Ohno, U.S. Pat. No. 4,001,390). This patent and all other cited patents are incorporated by reference herein.
Numerous methods for pan-coating pharmaceutical tablets have been developed and are summarized in Pharmaceutical Dosage Forms: Tablets, Volume 3 (eds. Lieberman and Lachman, 1982, Marcel Dekker). They include sugar-coating techniques, solvent film coating, aqueous film coating, delayed release coating, and granule coating. Pulverized medicine may also be wrapped in a transparent, glossy, resistant, soluble or semi-permeable film as provided by Motoyama et al. (U.S. Pat. No. 4,154,636).
Pharmaceutical tablets have been coated for a variety of reasons, including masking objectionable flavors or odors, protecting unstable tablet compositions, providing protection of the tablet through the stomach with enteric coatings, improving the appearance of the tablet or separating medicine ingredients into a core segment and coating segment.
Aspirin tablets or other tablets that are powdery, easily dissolved and friable have been treated with a variety of coatings to keep them from dissolving too soon (John et al., U.S. Pat. No. 4,302,440). Also, other polymers in non-aqueous vehicles have been used to granulate tablets (Gans et al., U.S. Pat. No. 3,388,041) or to coat onto tablets (Jeffries, U.S. Pat. No. 3,149,040) to protect from dissolving in the stomach or to delay the drug's release. Other non-aqueous film-coating systems have been designed to be applied to a variety of tablets containing a variety of active ingredients as illustrated by Singiser, U.S. Pat. No. 3,256,111 and Brindamour, U.S. Pat. No. 3,383,236. The aqueous coating processes are environmentally more safe than the non-aqueous processes, which involve the use of organic solvents in film-coating solutions. Thin film coatings, which do not alter the dissolution characteristics of the tablet, may be readily formed using aqueous film-coating processes. Unless adequately thick or insoluble coatings are used, most coatings are not capable of effectively masking the strong objectionable bitter taste of triprolidine hydrochloride or other compounds with similar properties.
Previous attempts to solve the problem of masking the taste and odor of active ingredients in tablet form have led to slow-dissolving coatings, thicker coatings, and sugar coatings (sucrose or mannitol). Although an unflavored soluble film-coating may normally be adequately thick to effectively mask the objectionable bitter taste of triprolidine and other compounds with similar properties, persons who have difficulty swallowing such tablets may find that even tablets having adequately thick soluble film-coatings may partially dissolve in the mouth, thus decreasing the effectiveness of the coating in masking the objectionable flavor.
Tablets have been coated with compositions containing sugar or sugar substitutes to make them more palatable as well as to improve their appearance in some cases. One sugar-coating pan process involves applying a first water-repellent layer, a subcoat and a sugar coat, and coloring and polishing the sugar-coated tablet. The sugar-coating pan process is time-consuming and greatly increases the tablet size. It is believed that the prior sugar coatings do not include use of strong pleasant masking flavors to better disguise the bitter taste.
Although it is believed that strong, masking flavorings such as fruit or mint flavorings have not been used with tablet coatings, some flavorings have been used in liquid medicines. Liquid medicines having strong tastes have been mixed with sweet and/or flavored substances such as fruit flavors to mask the taste. For other oral, solid dosage forms, medicinal compounds have been mixed with waxy materials and water-swellable high molecular weight materials to mask objectionable tastes.
It is believed that the previous uses of flavorings or fragrances in thin-film coatings for pharmaceutical tablets have not utilized aqueous spray coatings and have included mild flavored or low concentrations of flavored ingredients having pronounced, characteristic fragrances for relatively mild-flavored medicines, especially those having an objectionable odor. Such flavored or fragrant coatings include a pressed film coating incorporating 0.5% orange essence to impart the smell of an orange (Motoyama, U.S. Pat. No. 4,154,636) and a non-aqueous air spray coating containing 5.2% ethyl vanillin on a vitamin tablet core (Singiser, U.S. Pat. No. 3,256,111). An aqueous film coating for aspirin in which unspecified flavorings were mentioned as optional additions is found in John, U.S. Pat. No. 4,302,440.
Another major function of tablet coatings has been to aid in tablet identification. Thus, the use of coatings containing pigments on tablets provides a way to identify tablets by color. Pigment addition also allows the tablets to have a more uniform and pleasing appearance. Tablet coatings comprising a colored film coating have been prepared, for example, by dispersing an anhydrous pigment suspension in a polymer solution (Signorino U.S. Pat. No. 3,981,984). However, persons with impaired vision often have difficulty in being sure that they are taking the correct medicine even with color-coded tablets.